Stain-resistant earthen articles, grout and floor and wall surfaces composed thereof

ABSTRACT

Thin, strong, composite masonry-plastic articles having an earthen body impregnated with an in situ polymerized plastic and a drying oil or semi-drying oil; a mastic for forming a stain resistant grout comprising about 70% to 80% sand and about 20% to 30% of a plastic binder; stain-resistant wall and floor structures comprising said composite articles and grout; and a method for installing such wall and floor structures are described.

This is a divisional of application Ser. No. 06/292,018 filed Aug. 11,1981, now U.S. Pat. No. 4,407,884 issued Oct. 4, 1983.

BACKGROUND OF THE INVENTION

The use of earthen tiles, bricks or similar articles as a floor or wallcovering in high traffic areas has become very popular in recent years.However, such floor covering materials are subject to the seriousdisadvantage that they are easily stained or discolored and, therefore,do not retain an attractive appearance unless sealed in some way toprevent such staining. Previously available sealing materials andtechniques have provided a protective layer on the surface of the floorcovering which is subject to wear, particularly in high traffic areas,and must, therefore, be periodically renewed. This, of course, entailssubstantial expense in material and labor to maintain an acceptableappearance for such floors.

Moreover, previously available floor tiles have necessarily beenrelatively thick, e.g. from about 1/2" to about 2" in order to providesufficient breaking strength. Such thicknesses cause problems ininstallation especially in remodeling work and also add to the costshipping the tiles due to the added weight.

Another serious problem with floors generally composed of floor tiles,is that they are generally installed with a cement type grout, which isalso very susceptible to staining and must, therefore, also be sealed.

THE PRIOR ART

Traditional earthen flooring materials such as stone, cement, brick andgypsum floor and wall tiles, and bricks required sealing to preventstaining and discoloration by a wide variety of materials capable ofpenetrating the porous tiles or bricks and then drying or curing in situto fill and seal the pores of the material and provide a film or layerof impregnant on the surface of the tile or brick. Such sealers havegenerally comprised a resin of some sort in a volatile liquid vehiclewhich evaporates or dries to leave a resinous film. Such resinous filmsprovide some protection and have proven fairly satisfactory for home usein low or moderate traffic areas, but are not sufficientlywear-resistant for high traffic areas such as those in public orcommercial buildings.

A process for imparting long lasting gloss, color depth properties, andstain resistance to wood tiles for floor and wall covering use isdescribed in Bosco U.S. Pat. No. 3,808,032, issued Apr. 30, 1974. Thisprocess comprises impregnating the wood with a monomer polymerizable byorganic free radicals, polymerizing the monomer in situ in the wood, andthereafter coating the surface of the wood with a penetrating solutioncomprising a drying oil or a semi-drying oil. The polymerization isaccomplished by exposure to ionizing radiation, and is catalyzed byincluding from about 0.01 to about 0.5 weight percent of a free radicalpolymerization agent in the monomer. The reaction is accelerated byheat. Suitable monomers include methyl methacrylate, vinyl chloride,vinyl acetate, styrene and mixtures of these monomers. Suitable dryingoils include soybean, linseed, tall, tung, peril a, oitica, cottonseed,corn, sunflower and dehydrated castor oil and mixtures of these oils.The preferred drying oil is doubly boiled linseed oil. The oils areapplied in amounts of about 0.5 to about 2.0 gallons per 6000 squarefeet of wood surface. The penetrating solutions comprise the oil of anorganic hydrocarbon solvent in an oil to solvent ratio from about 3:1 to1:3. The preferred solvents are naptha, Stoddard solvent and petroleumether. From about 0.01 to about 1 weight percent of a siccative agentsuch as cobalt, lead, zinc and manganese salts may be added to thepenetrating solution. In this way, wood tiles are obtained which have apermanent gloss, water spotting resistance and stain resistance.

A similar process for making wood-plastic composite tiles is describedin Bell U.S. Pat. No. 3,808,030, also issued on Apr. 30, 1974. In thisprocess a halo-organophosphorous composition is included in the monomerbefore polymerization to impart flame retardancy and to prevent lakingof the impregnant on the surface of the tiles. It is also noted that thepenetration of the polymerized plastic is so deep into the wood that thetiles may be sanded deeply before finishing by buffing without damagingthe impregnated plastic. This patent also described preferred finishingtechniques to produce floor tiles having good wear and stain resistance.

Barrett U.S. Pat. No. 3,721,579 issued Mar. 20, 1973 describes methodsand apparatus for impregnating wood or concrete substrates with amonomer and polymerizing the monomer in situ by irradiation. This patentteaches how to control the temperature and degree of polymerization inorder to polymerize the monomer in the substrate without polymerizingthe monomer both surrounding the substrate and how to avoid vaporizingthe moisture in the wood. This patent also lists a large number ofsuitable monomers for impregnation of the substrates. A large number ofsubstrates are also suggested, including preformed concrete shaped inthe form of flooring or wall tiles.

Welt U.S. Pat. No. 3,709,719 issued Jan. 9, 1973, describes a processfor making a masonry-plastic material having a glossy, smooth surface,improved wear and resistance properties, and a low porosity, whichcomprises impregnating a masonry material with a monomer whichpolymerizes on exposure to radiation. The masonry material is insertedin a bath of monomer and the monomer in the masonry material ispolymerized in situ by exposing the bath to a source of radiationsufficient to polymerize the impregnated monomer but insufficient topolymerize the monomer bath.

In view of the foregoing, it is apparent that the art has attempted tosolve the problem of staining and discoloration of floor tiles used inhigh traffic areas. However, the art has not previously solved theproblem of maintaining a floor of such earthen or brick tiles inattractive condition, since it has not found any way to prevent thegrout between the tiles from becoming stained or discolored. Therefore,even the use of stain resistant brick or masonry tiles fail to provide afloor having a long lasting attractive appearance since the groutingsoon becomes discolored.

It is an object of the present invention, therefore, not only to providerelatively thin brick or earthen floor tiles but strong and lightearthen floor tiles of improved stain resistance, but also to providestain resistant grout and an installed grouted floor or wall which willremain undamaged and free of stains or discoloration for prolongedperiods of time even in high traffic areas.

It is another object of the invention to provide a thin, stain resistantearthen floor which can be installed in a single simple operation.

SUMMARY OF THE INVENTION

The present invention relates to composite earthen-plastic articles suchas tiles or bricks having improved stain resistance and strength, to anovel mastic composition for installing the earthen-plastic articleswhich sets up to form a stain-resistant grout, and to the resulting wallor floor surfaces which are suitable for use in high traffic areas andwhich remain attractive for long periods of time without specialmaintenance since both the earthen-plastic articles and the grout makingup the exposed surfaces are stain-resistant.

The stain-resistance and improved strength of the earthen-plasticarticles is achieved by double impregnation of the materials. Thearticles are first impregnated with a suitable polymerizable monomerwhich is then polymerized in situ in the body of the earthen articleaccording to methods known per se, in the art. This impregnation notonly improves the stain-resistance of the articles but also theirstrength, thus permitting the use of relatively thin articles even inhigh traffic areas. The resulting plastic-impregnated earthen tile orbricks are then doubly impregnated with a penetrating solution of adrying oil or semi-drying oil to further improve their stain-resistance.This double impregnation extends deeply into the body of the articlewhich may, therefore, be ground to achieve a smooth surface and thenbuffed to achieve a high polish or any other desired surface finish. Theresulting articles are highly stain-resistant and exceed the ANSIspecification for strength, thus making them suitable for use in pavingthe walls and floors of high traffic areas. The finished articles may bederived from any suitable earthen starting material including, withoutlimitation, fired clay based brick, unfired non-clay brick derived fromgypsum, pumice or the like, cement compositions derived from Portlandcement, natural stone, slate or marble, turquoise, coral or any otherfossil, shell or other earthen material having acceptable strength whensupported on a suitable substrate, subflooring or wall board.

DETAILED DESCRIPTION OF THE INVENTION THE EARTHEN-PLASTIC ARTICLES

The earthen-plastic articles of the invention having improvedstain-resistance may be derived from any known earthen article orcomposition; the term "earthen" as used herein being intended to meanany solid material derived from the earth or found in nature or similarsynthetic materials which are sufficiently porous to be impregnated asdescribed below. Such materials include without limitation, natural orsynthetic stone, slate, marble or turquoise, coral or other fossils orshells, concrete, Portland or other cement compositions, earthenware ofany type including fired or unfired clay base or non-clay based bricks,or any other earthen composition. The articles are preferably initiallyformed in the desired shape, although they may be cut to shape afterimpregnation. Generally, the articles are formed into thin tiles orbricks of the desired size, shape and thickness before impregnation. Theterm "thin" as used herein means less than about 1/2", e.g. about 5/16".

The earthen articles are then impregnated with a suitable polymerizablemonomer and the monomer is then polymerized in situ within the earthenarticle to form the first stage earthen-plastic articles of theinvention. These articles are then impregnated with a penetratingsolution of a drying oil or semi-drying oil and then finished as desiredby grinding and buffing to form the finished stain-resistantearthen-plastic articles. All of this is accomplished in the same way ashas been taught in the art previously with respect to wood articles inBell U.S. Pat. No. 3,808,030 and Bosco U.S. Pat. No. 3,808,032, bothissued Apr. 30, 1974; the entire disclosure of each of said patentsbeing incorporated herein by reference.

The impregnation with the selected monomer is carried out in animpregnation/irradiation vessel, known in the art per se, of suitabledimensions such as a vessel of about 1 ft×2 ft×18 ft. After introducingthe articles to be impregnated to the vessel, it is placed in a 3'diameter vessel for impregnation. The vessel is then evacuated, suitablyto about 20-30 millimeters mercury pressure for a suitable period, e.g.,about 2 hours. The impregnant is then introduced through suitablevalving to completely immerse the articles. The head space is thenfilled with an inert gas such as nitrogen under pressure, suitably about80 psi for a suitable period of time, e.g. 3 hours. The process gasshould be free of oxygen since oxygen inhibits the radiationpolymerization reaction. The period required for suitable impregnationwill, of course vary with the earthen material depending upon itsporosity, the viscosity of the monomer and other factors and may bedetermined for each material by trial and error. Generally speaking, animpregnation period of about 2 to about 3 hours is generally adequate.This time and other conditions may be varied to control the depth ofimpregnation as desired. The viscosity or thickness of the monomer mustbe such that it will penetrate the pores of the particular material tobe impregnated.

The pressure is then reduced and the excess monomer is drained from thevessel. The vessel containing the monomer-impregnated articles is placedin the irradiator.

The pool irradiator arrangement may suitably be a tank about 26 feetdeep or more, about 50 feet long and about 22 feet wide filled withwater. A standard irradiator unit such as a "NEPI" unit or an "NPI" unitmay suitably be placed on the floor of the pool irradiator. Suchirradiator source units available from NUMEC produce 500,000 curies ofirradiation from cobalt 60 and comprise 37 inch pencils arranged in aplaque 12 feet by 9 feet. Any other source unit providing equivalentgamma radiation may be employed. Such an irradiator arrangement operatesat ambient temperature and pressure. Handling means are also providedfor lowering the canister to the proper pool depth and orienting withinthe zone of irradiation.

The canister is first preferably flushed several times to purge it ofoxygen. This is suitably accomplished by the use of nitrogen at about 5psi. The cover of the canister is then sealed and the canister islowered into the water in the pool and passed slowly through theirradiation zone close to the source of irradiation. Irradiation iscarried out for a predetermined period of time, for example, about 10hours and provides a dose of about 1.7 MRAD. The period of treatment anddosage will, of course, vary with the monomer and substrate beingimpregnated.

Generally speaking, the dosage required to convert a monomer to apolymer varies with the square root of the radiation dose rate. Thedosage requirement for complete polymerization of the monomer in themasonry articles is determined by such factors as the type of earthen inquestion, the type and concentration of the monomer, the presence ofimpurities, such as oxygen for example, in the impregnant or in themasonry or environment and the use of irradiation activators.

The radiation-induced polymerization causes the monomer molecules tobecome linked throughout the earthen article forming a network ofpolymer that envelops the pores of the components thus sealing them inplastic and providing stain resistance. Radiation-inducedpolymerization, proceeds by a free radical process, and does not requirethe addition of either heat or catalyst, although both may be used ifdesired. However, inasmuch as the radiation itself acts as a catalyst,it offers a method of controlling the exothermic polymerization reactionin the substrate, which is difficult to achieve if catalyst and heat areemployed.

IMPREGNANT MATERIALS

Vinyl monomers are highly suitable, methyl methacrylate (MMA), beingespecially preferred, since it is readily available and easilypolymerizable. The monomer may be inhibited by Butylate HydroxideToluene (BHT) at 35 ppm or by other inhibitors known to the art. Knownactivators may also be used if desired. Other vinyl monomers are alsovery useful including the acrylates which are desirable for theirelastomeric properties. Suitable examples are ethyl acrylate co-polymerswith vinylidene chloride or acrylonitrile. Acrylonitriles and styrenesare also suitable monomers for some applications. The styrenes, however,require relatively large radiation doses as much as 20 times that formethyl methacrylate. Vinyl chloride is also attractive because of itslow cost, although it presents handling difficulties known to the art.These monomers may also be mixed as desired and may also be diluted withinert fillers such as silica or bentonite or the like to reduce cost.

A wide variety of other additives may be used such as water repellants,dyes, fungicides, odorants, bacteriostats and the like.

Additives may also be used to reduce the heat of polymerization,radiation requirements and/or the cost of the impregnant. Certainplasticizers can be expected to provide one or all of the foregoingadvantages: for instance sebacates, adipates, polychlorinated phenyls orphthalates.

Monomers used for wood and Portland cement impregnation will not workfor most earthen materials. The pore structure is such that the monomerwill run from the structure and incomplete impregnation will result.

A special methyl methacrylate monomer was developed using varyingamounts of a thickening agent. The amount will vary according to thestarting material. Thickening agents include long chain acrylics,phosphorus organics, or other compatible polymer materials.

The mastic of the invention is largely composed of sand but has stainresistance imparted thereto by the unique combination of about 20 toabout 30% of a suitable stain-resistant plastic binder, preferably anacrylic binder such as polyvinylacetate, and several active materials.These materials include a surface active agent to aid in achieving anintimate wetting or contact with the bricks, tiles or otherearthen-plastic articles; a lubricant for the sand-binder composition,and plasticizer to impart strength. It is also desirable to add an agentto prevent freezing of the mastic on storage or during shipping. Theresulting mastic when used to install the stain-resistantearthen-plastic articles sets up in about 4 to about 24 hours onexposure to the air to form a solid grout which is also highly stainresistant.

The resulting wall or floor surfaces of the invention are suitable foruse even in very high traffic areas, resist damage, and retain anattractive appearance despite such traffic for prolonged periods of timedue to the fact that articles are very strong and both theearthen-plastic articles and the grout are highly stain-resistant.

Generally speaking, the loading of impregnant plastic will suitably varyfrom about 5 to 30% and preferably about 10 to 25% plastic based on theweight of the total earthen-plastic article after polymerization.

EXAMPLE 1

Three hundred fifty square feet of earthen tiles (98% Pumice) wereloaded into the impregnation irradiation cannister. Tile size35/8"×75/8"×5/16" thick. After a two hour vacuum of 27" of Hg, themonomer was introduced. Monomer consisted of 15% thickening agent, 3%crosslinker and 82% methyl methacrylate. A nitrogen over pressure of 80psi was maintained for 2 hours to force the liquid into the pores.Excess monomer was drained from the vessel and the vessel and productwere irradiated with a cobalt 60 source to a total dose of 1.7 megarads.

The resulting product consisting of 74% earthen materials and 26%plastic was processed through two single head sanders utilizing 30 and50 grit paper. The sanded composites were continuously contacted with aprint roller to deposit double boiled linseed oil on the surface.Application rate was 6,000 square feet per gallon. After the oilapplication, the samples were buffed and boxed. The resulting productwas stain resistant, and had structural properties that exceeded ANSIspecifications. Thus a product that under no situation could be used asa flooring material, was converted to a superior flooring material.

EXAMPLE 2

Four hundred twenty five square feet of thin fired clay base bricks wereloaded into the impregnation irradiation cannister. Brick size was21/4"×71/2"×5/16". After a two hour vacuum of 27" of Hg, the monomer wasintroduced. Monomer consisted of 3% crosslinking agent and 97% methylmethacrylate. A nitrogen over pressure of 80 psi was maintained for 3hours to force the liquid into the pores. Excess monomer was drainedfrom the vessel and the vessel and product was irradiated with a Cobalt60 source to a total dose of 1.7 megarads.

The resulting product consisting of 90% earthen materials and 10%plastic was processed through two single head sanders utilizing 30 gritpaper. The sanded composites were continuously contacted with a printroller to deposit double boiled linseed oil on the surface. Applicationrate was 4,000 square feet per gallon. After the oil application thesamples were buffed and boxed.

The resulting product was stain resistant, and had structural propertiesthat exceeded ANSI specifications. Thus a 5/16 inch thick product thatcould not be used as a flooring material was converted to a superiorflooring material.

EXAMPLE 3

Three hundred square feet of coral tile were loaded into theimpregnation irradiation vessel. Tile size was 6"×6"×3/8". After 2 hoursvacuum of 27" of Hg, the monomer was introduced. Monomer consisted of10% thickening agent, 3% crosslinker and 87% methyl methacrylate. Anitrogen over pressure of 80 psi was maintained for 2 hours to force theliquid into the pores. Excess monomer was drained from the vessel andthe vessel and product were irradiated with a Cobalt 60 source to atotal dose of 1.7 megarads. The resulting product consisting of 76%earthen materials and 24% plastic was processed through two single headsanders utilizing 30 and 50 grit paper. The sanded composites werecontinuously contacted with a print roller to deposit double boiledlinseed oil on the surface. Application rate was 5,000 square feet pergallon. After the oil application the samples were buffed and boxed. Theresulting product was stain resistant, and had structural propertiesthat exceeded ANSI specifications. Thus a product that under nosituation could be used as a flooring material was converted to asuperior flooring material.

DOUBLE IMPREGNATION

The earthen-plastic articles obtained as above have some stainresistance but that property is greatly improved by a secondimpregnation of the article with a penetrating solution of a drying oilor semi-drying oil. While such a second impregnation has been suggestedpreviously for wood articles in Bosco U.S. Pat. No. 3,808,032 issuedApr. 30, 1970, it was not to be expected that impregnation with dryingoils or semi-drying oils would have a beneficial effect upon the stainresistance of earthen articles.

In accordance with the invention, the earthen-plastic composite istreated with a small, controlled amount of a drying or semi-drying oil.The result of this treatment is to further coat the pores of theproducts. The drying or semi drying oil becomes absorbed in the pores,and undergoes a combination of oxidation and condensation reactionswhich result in a mixture of high molecular weight compounds.

Suitable drying and semi-drying oils include soybean, linseed, tall,tung, perilla, oitica, cottonseed, corn, sunflower, dehydrated castoroil and the like. The preferred drying oil is doubly boiled linseed oil.

While it is greatly preferred to apply the process of the invention to acontinuous process at the point of manufacture of the earthen-plasticcomposites, it can also be applied very successfully to earthen-plasticcomposite floors or walls which have already been installed. Thepreferred processes are somewhat different when performed "in field,"and at point of manufacture of the composites. When "in field", it ispreferred to apply the drying oil or semi-drying oil to theearthen-plastic composite in a solvent carrier. Suitable solventcarriers include low boiling petroleum distillates, such as mineralspirits, naphtha (VM&P type), Stoddard solvent, petroleum ether and thelike. The volume ratio of drying oil to solvent carrier is suitably fromabout 3:1 to 1:3 and preferably from about 1.5:1 to 1:1.5. The preferredsolvent carrier is Stoddard solvent. After application, the solventcarrier vaporizes, leaving the drying oil or semi-drying oil as acoating on the pores of the earthen-plastic article, but does not form acontinuous film over the entire surface of the composite.

Any suitable means for applying the required amount of formulation canbe used.

In the "in field" case, a sponge mop is one very suitable means,especially when the process is being applied to flooring compositesalready in place. The amount of drying oil and solvent carrierformulation applied is between one gallon per 1,000 square feet and onegallon per 2,500 square feet, preferably one gallon to between 1,300 and2,000 square feet.

In the "point of manufacture" case, the drying oil is supplied to thesurface of the earthen-plastic composite in amounts sufficient to coatthe individual surface pores, but insufficient to coat the entiresurface, preferably from about 0.5 to about 2.0, more preferably fromabout 0.9 to about 1.1 gallons of drying or semi-drying oil per 6,000square feet of earthen-plastic composite surface. Preferably, the dryingor semi-drying oil is applied in a continuous process at speeds andconditions designed to insure application of the desired amount offormulation per square foot. One suitable means of continuousapplication is a rubber type print roll having a pattern embossedthereon to "print" the formulation in a pattern as the masonry-plasticcomposite is passed under the roller. The pressure on the rollerpreferably can be adjusted to help control the application of thedesired amount of formulation.

Optionally, a siccative agent is incorporated in the formulation toaccelerate the polymerization of the drying or semi-drying oil after itis applied to the masonry-plastic composite surface. Suitable siccativeagents include heavy metal salts, such as naphthenates or neodecanatesof cobalt, lead, manganese, or zinc and other drying accelerators.Mixtures of salts are especially suitable and are preferred. Preferredamounts of siccative agent are from about 0.01 to 1 weight percent basedon the weight of the formulation, and more preferably from about 0.05 to0.5 weight percent.

While not intending to be bound by any theory of the invention, it isthought that the drying or semi-drying oil becomes absorbed in the poreson the surface of the composite and polymerizes to form awater-resistant finish. Without the drying or semi-drying oil treatment,water coming in contact with the composite surface has a tendency topenetrate the pores, adversely affecting the appearance, gloss andbeauty of the composite. The drying or semi-drying oil treatmentpermanently prevents water spots and water staining on theearthen-plastic articles.

After application of the formulation in accordance with the process ofthe invention, it is preferred to again buff the surface to remove anyexcess material. One suitable means for this buffing is use of a nylonpad. To obtain the most aesthetically pleasing properties, it ispreferred to buff one more time with a nylon pad to polish the floor orwall after about 24 hours from the application of the formulation.Optionally, heat and pressure are applied during the buffing and havebeen noted to have a beneficial effect.

STRENGTH IMPROVEMENT AND OTHER PROPERTIES

It has been found that the breaking of the new earthen-plastic articlesis not only greatly increased over that of the unimpregnated startingmaterials, but exceeds by over 60% the (ANSI) Specification for suchflooring materials. Moreover, the bonding strength and resistance towear of the new articles also greatly exceed the ANSI specifications.Still further, the moisture absorption of the new articles is far lessthan that permitted by the ANSI specifications.

More specifically, the properties of the new articles exceed the ANSIspecifications as shown in the table below.

    ______________________________________                                        PROPERTIES                                                                                ANSI                                                                          Specifi-                                                                             Articles of the Invention                                  Property      cation   F-Series   S-Series                                    ______________________________________                                        Bond Strength 50 psi   80 psi     80 psi                                      Moisture Absorption                                                                         <5%      <0.5%      1.3%                                        Break Strength                                                                              250 psi  500 psi    400 psi                                     Resistance-to-Wear                                                                          35       61         51                                          ______________________________________                                    

THE MASTIC AND GROUT

As noted above, the present invention also includes an improved masticcomposition for installing the stain-resistant articles which sets upinto a stain-resistant grout.

The new mastic is composed largely, i.e. about 70 to 80% by weight, ofan inert particulate filler such as a suitable sand or silica. The otheressential ingredient of the mastic is a stain-resistant plastic binderfor the sand which impart stain-resistance to the grout after it is set.The preferred binder is polyvinyl acetate although other equivalentpolymers may be employed. The mastic contains about 20 to 30% of such abinder.

Other active additives are included in the mastic. For example, it ispreferred to include a surface active agent to aid in wetting thesurfaces of the sand and articles with the mastic binder and impartsurperior stain resistance. Many non-ionic surfactants may be employedfor this purpose, the alkylphenyl polyether alcohols being especiallyuseful. The preferred surfactant, which may be used in amounts up toabout 0.5% or more, is octylphenoxypolyethoxyethanol which is availablecommercially under the trademark "TRITON X405". The material containsabout 40 monomer units per molecule.

It is also desirable to include a lubricant for the sand and binder.Suitable lubricants include the polymethyl siloxanes among othersknownto the art. The preferred lubricant is poly dimethyl siloxane which isavailable commercially under the trade designation "Silicone FluidSWS-101" from SWS Silicones Corporation of Adrian, Mich.

Another desirable component of the mastic is a plasticizer many of whichare known to the art. The preferred plasticizer is polyoxyethylene arylether which may be used in amounts up to about 0.5% or more and which isavailable under the trademark "PYCAL 94" from ICI Americas Inc. ofWilmington, Del.

The preferred binder as noted above, is polyvinyl acetate (PVA). Anespecially preferred PVA is a vinyl acetate homopolymer emulsionavailable under the trademark "VINAC XX-210 to 240" which has chemicalAbstract Registry number 9003-20-7. Other equivalent polyvinyls may alsobe employed if they bind the sand properly and impart stain-resistanceto the set grout.

The mastic may also contain various other additives to impart improvedproperties. One such is an anti-freeze stabilizer to prevent freezing ofthe viastic on a storage or shipping. The preferred anti-freeze agent isethylene glycol which may be used in amounts of up to about 1% or more.

INSTALLATION

The ease and simplicity of installation of the improved stain-resistantarticles and mastic providing stain-resistant grout constitute one ofthe primary advantages of the invention. Installation may be carried outon any suitably stable substrate such as a wood, plywood, masonry stoneor metal sub-flooring or wood, plywood, chip-board, dry wall or gypsumblock wall surface. The paste-like mastic composition is simply spreadon the substrate to a suitable thickness and the impregnated articles,whether tiles, bricks or other suitable shaped articles, are placed onthe wet mastic and imbedded therein by suitable pressure to forcedisplaced mastic up around the edges of the tile or brick. The usualgrout lines of desired width are left between adjacent tiles or bricks.Additional mastic may be troweled into the grout lines and leveled andsmoothed as necessary to provide sufficient grout between adjacent tilesor bricks. Excess mastic may be removed from the surface of the masonryarticles by wiping in known manner. The mastic is then allowed to set toform the stain-resistant grout and fully stain-resistant floor and wallsurfaces of the invention. While setting times will vary, in most casesfloors installed in this way can be walked on without damage after about4 to about 24 hours.

The floor and wall surfaces prepared in this way will provide excellentservice even in very high traffic areas and will remain undamaged,unstained, and attractive for long periods of time.

While the articles of the invention are normally installed with visiblegrout lines, they may also be installed edge to edge without visibleintermediate grout. For example, pumice or coral tiles may be closelymachined to permit closely fitting joints without grout therebetween;the only grout being below the tile adjacent the substrate.

What is claimed is:
 1. A stain- and wear-resistant wall or floor surfacecomprising:a plurality of composite earthen-plastic articles havingimproved stain-resistance and strength; said articles comprising aporous earthen body having a synthetic plastic polymerized in situtherein and being further impregnated with a penetrating solutioncomprising a drying oil or a semi-drying oil; said polymerized syntheticplastic being substantially uniformly distributed throughout saidearthen body; said drying oil or semi-drying oil also beingsubstantially uniformly distributed throughout said earthen body;whereby said articles have a substantially uniform compositionthroughout the thickness thereof with the pores substantially filledwith said plastic and oil to provide said stain-resistance; saidarticles being assembled in said wall or floor surface imbedded in alayer of stain-resistant grout surrounding the edges of said articlesand holding them in position in said surface; whereby a wall or floorsurface is provided having improved breaking strength andstain-resistance.
 2. The surface of claim 1 wherein the drying oil isselected from the group consisting of soybean, linseed, tall, perilla,oitica, cottonseed, corn, sunflower, and dehydrated castor oil, ormixtures thereof.
 3. A surface of claim 1 wherein the articles are lessthan about " thick and have a breaking strength in excess of the ANSIspecification.
 4. The surface of claim 5 wherein the polymer is derivedfrom a monomer selected from the group consisting of methylmethacrylate, vinyl chloride, acrylonitrile, vinyl acetate, and styrene,or mixtures thereof.
 5. The surface of claim 4 wherein the polymer ispolyvinyl acetate.
 6. The surface of claim 1 wherein the articles have abody of earthenware.
 7. The surface of claim 6 wherein said earthenwarebody is fired clay base brick.
 8. The surface of claim 6 wherein saidearthenware body is unfired non-clay brick.
 9. The surface of claim 8wherein the brick comprises gypsum.
 10. The surface of claim 8 whereinthe brick comprises pumice and a cementitious binder therefor.
 11. Thesurface of claim 8 wherein the brick comprises coral or turquoise. 12.The surface of claim 8 wherein the earthen body comprises Portlandcement.
 13. The surface of claim 8 wherein the non-clay brick isimpregnated before said in situ polymerization with a pre-polymercomprising about 5 to about 10% bentonite.
 14. A stain andwear-resistant wall or floor surface of claim 1 wherein said grout isobtained from a mastic comprising:up to about 80% sand or silica; up toabout 30% or more stain-resistant plastic binder, and a minor amount ofa surface active agent which enhances contact between said sand orsilica and said binder and which imparts added stain-resistance to thegrout obtained from said mastic on setting thereof; said percentagesbeing by weight of the total mastic composition.
 15. A surface of claim14 wherein said mastic also comprises a lubricant for said sand orsilica and a plasticizer for said binder.
 16. A surface of claim 14 inwhich the binder in the mastic is a vinyl homopolymer.
 17. A surface ofclaim 14 in which the binder in said mastic is polyvinyl acetate.
 18. Astain- and wear-resistant wall or floor surface comprising;a pluralityof earthen-plastic articles having improved stain-resistance andstrength; said articles comprising a porous earthen body having asynthetic plastic polymerized in situ therein and being furtherimpregnated with a penetrating solution comprising a drying oil or asemi-drying oil; said plastic and oil being uniformly distributedthroughout the volume of said articles to impart strength andstain-resistance thereto; said articles being assembled in said surfaceimbedded in a layer of stain resistant grout surrounding the edges ofsaid articles and holding them in position in said surface; said grouthaving been obtained by setting and hardening of a mastic compositioncomprising:up to about 80% sand or silica; up to about 30% or morestain-resistant plastic binder; and a minor amount of surface activeagent which enhances contact between said sand or silica and said masticbinder and which imparts added stain-resistance to the grout obtainedfrom said mastic on setting thereof; said percentages being by weight ofthe total mastic composition.
 19. A surface of claim 18 wherein saidmastic also comprises a lubricant for said sand or silica and aplasticizer for said mastic binder.
 20. A surface of claim 18 in whichthe binder in the mastic is a vinyl homopolymer.
 21. A surface of claim18 in which the binder in said mastic is polyvinyl acetate.
 22. Asurface of claim 18 wherein the surface active agent is non-ionic, thelubricant is polymethylsiloxane and the plasticizer is a polyoxyethylenearyl ether.
 23. A surface of claim 18 in which the surface active agentis octylphenoxypolyethoxyethanol and is present in an amount of up toabout 0.5% or more; the lubricant is polydimethylsiloxane in an amountup to about 0.9%; and the plasticizer is present in an amount up toabout 0.5% or more.
 24. A surface of claim 18 in which the masticcomprised about 65-70% sand; about 30-32% vinyl acetate homopolymeremulsion; about 0.5% octylphenoxypolyethoxyethanol; about 0.5%polyoxyethylene aryl ether; about 0.5% polydimethylsiloxane; and about1% ethylene glycol.